1. Field of the Invention
This invention relates to electronic article surveillance systems (EAS) and markers for use therein. More particularly, the invention provides an integrated hybrid tag which can be detected by both a magnetic harmonic article surveillance system and a radio frequency article surveillance system.
2. Description of the Prior Art
The problem of protecting articles of merchandise in stores against shoplifting has been the subject of numerous technical solutions. Among these solutions is securing a tag or marker to an article to be protected. The marker responds to an interrogation signal from transmitting apparatus situated at an exit door of the store. A receiving coil on the opposite side of the exit door receives a signal produced by the marker in response to the interrogation signal. The presence of the response signal indicates that the marker has not been removed or deactivated by the cashier, and that the article bearing it may not have been paid for or properly checked out.
A number of different types of markers have been widely used. In one type, the functional portion of the marker consists of an electrical resonant circuit. When placed in an electromagnetic field transmitted by the interrogation apparatus, the resonant circuit marker causes an increase in absorption of the transmitted signal in order to reduce the signal in the receiving coil. The detection of the signal level change indicates the presence of the marker. A commercially used marker of this type is operated at radio frequency (RF) region, e.g. 8.2 MHz, and referred as an RF tag.
A second type of marker consists of an elongated element of a ferromagnetic material having a high magnetic permeability placed adjacent to a second element of a ferromagnetic material having a higher coercivity than the first element. When subjected to an electromagnetic radiation at an interrogation frequency, the marker causes high harmonics of the interrogation frequency to be developed in the receiving coil. Detection of such harmonics indicates the presence of the marker. Deactivation of the marker is accomplished by changing the magnetization state of the second element. Thus, when the marker is exposed to a dc magnetic field, the magnetization state in the second element changes and the amplitude of the harmonic chosen for detection is significantly changed. This change can be readily detected in the receiving coil. This is a typical magnetic harmonic EAS tag. A commonly used interrogation frequency for the harmonic tag is in the range of a few thousand Hertz.
The most economic way to affix the anti-theft marker onto merchandise is during the manufacturing process on the production line. However, both the radio frequency tag and the magnetic harmonic tag described above are widely used in various retail stores. At the merchandise manufacturing stage, there is no knowledge of which store the merchandise is going to and what type of detecting system will be used. As a result, the manufacturer would have to put both types of tags on the merchandise. Also, at the check-out counter of a retail store, the cashier would have to deactivate both tags to eliminate false alarm even though the store only uses one kind of detection system. Installing two separate markers at the merchandise manufacture would cause operational complications and overall cost increase.
The object of this invention is to make a deactivatable hybrid marker that can be detected by both RF detection and harmonic detection systems. One type of a hybrid marker was disclosed in French Pat. No. 2,701,146 issued in 1994. However, in that patent, the hybrid marker merely consists of two types of markers, i.e. an RF marker and a harmonic marker, arranged on one substrate. The RF part of the marker and the harmonic part of the marker are separated from each other in the proposed design. Also, there is no deactivation function designed.
The present invention provides an integrated hybrid marker. The harmonic part of the marker is an active part of the RF resonant circuit. Also, the present hybrid marker can be deactivated in a single process.
The present invention provides an integrated hybrid marker comprising a harmonic element made of a strip of a high magnetic permeability material which is inserted into a RF circuit as an active part of the resonant circuit. The electrical contact between the element and the rest of the circuit is achieved by using conductive paste material. The deactivation of the marker is accomplished by employing another element of a magnetic material having a high coercivity.
When placed in a RF interrogation field, the hybrid marker causes an increase in absorption of the transmitted signal reducing the signal in the receiving coil of the RF surveillance system. When placed in an interrogation zone of a magnetic harmonic article surveillance system, the marker generates high harmonics of the interrogation frequency that can be detected by the receiver of the surveillance system. The hybrid marker can be deactivated in both RF and harmonic functions by a single process.